hot standby router protocol (HSRP)
The Hot Standby Router Protocol (HSRP) is a Cisco proprietary protocol designed to ensure high network availability. HSRP routes IP traffic from hosts onto Ethernet networks without relying on the availability of a single router.
This feature is especially useful for those hosts that do not support a router discovery protocol such as Internet Control Message Protocol( ICMP) or ICMP Router Discovery Protocol( IRDP) and are unable to switch to a new router if the selected router fails or is in the process of being reloaded. Without this functionality, a router that loses a default gateway due to a router failure will not be able to communicate with the network.
The HSRP protocol, similar to the standardized Virtual Router Redundancy Protocol( VRRP), ensures that only one interface with a virtual MAC address and the virtual IP address are active at any given time. The protocol works with Ethernet, Token Ring or FDDI and is described in RFC 2281.